1. Field of the Invention
The invention concerns a process for operating a vehicle transmission, particularly for control of an automatic vehicle transmission, and also a control or regulating system for conducting the process.
2. Description of Prior Art
Processes for operating or for control of automatic vehicle transmissions are already known from the following documents:
(1) DE 1,932,986 C PA1 (2) DE 3,205,767 C PA1 (3) EP 0 176,750 B2 PA1 (4) EP 0 435,372 B1
In automatic vehicle transmissions, it is known how to adjust the pressure of the operating medium, which serves for actuating the friction elements of the transmission, as a function of different operating parameters of the motor vehicle. In the process disclosed in DE 1,932,986 C, pressure is adjusted by means of an electronic control via pre-given pressure characteristics. An equilibration of parameter changes as a consequence of serial scatter or alternation effects cannot be achieved thereby. Friction values of discs, characteristics of pressure controllers or springs, as well as the momentum yielded by the engine, however, are continually subjected to this type of scatter, whereby, on the one hand, fluctuations in the quality of shifting have been produced, but on the other hand, high requirements are placed on tolerances of the parts applied or used. This has a very unfavorable effect on cost.
In the design disclosed in DE 3,205,767 C, closed control circuits were used. These, however, have the disadvantage that a regulated quantity calculating the necessary dynamics is required. Basically, stability problems are to be expected in the control system of engine transmissions due to the dead times present in the entire operating leg, and thus clear repetivie errors must be taken into the bargain before the control can be correctly engaged, and this is reflected in poor comfort during shifting.
A pressure controller for an automatic transmission control for vehicles is known from DE 3,025,054 A1, in which a desired shift time is applied for changing gears as a function of the load. The actually occurring shift time is measured and compared with the stored theoretical shift time. Fluctuations occur hereby, a correcting value is entered in a correcting register, which is added in a change of gear to pressure characteristics, which originally are stored in memory and serve for the purpose of controlling the pressure during the change in gear.
In the case of a process for the electronic control of an automatic vehicle transmission, as described in EP 0 176,750 B2, correcting values are calculated and applied as a function of the load and rpm, so that an exact adaptation to different load [and] rpm conditions can be produced. The theoretical and actual values for the characterizing quantities as well as the correction values formed are placed in load-rpm characteristic diagrams, whereby the actual values are formed by taking the mean of the individual values from several shift processes, so that the previous correction value is maintained until the averaging process is completed, and after conducting the correction, the actual values for the mean are referred to the theoretical values for modifying the correction value.
A process is described in EP 0 435,371 B1 for controlling the change in an automatic transmission of a vehicle from a torque transmission device operated by fluid pressure and transmitting reduced torque, which device is assigned to low speed conditions, up to a torque transmission device operated by fluid pressure and transmitting an increasing torque, which [device] is assigned to high speed conditions, if the engine choke is essentially closed. The outgoing torque transmission device is thus simultaneously or essentially simultaneously disengaged when the incoming torque transmission device is engaged. The transmission has an input, an output, and a turbine, which is coupled with the drive engine by means of the input. The process described in this publication thus comprises the following named steps. The filling trough is applied at the incoming torque transmission device for a [certain] filling time in order to fill the incoming torque transmission device essentially with operating fluid. The turbine speed runup is detected on the basis of an initial slippage of the torque transmission device transmitting the reduced torque, and a synchronization of the incoming torque transmission device on the basis of the turbine speed and of the output speed is established, and the change is then completed when synchronization is detected. Thus a lower pressure is applied to the outgoing torque transmission device for a time that is less than the filling time and then the outgoing torque transmission device is emptied of operating fluid. If a turbine speed runup is detected, a passage through one control loop is produced. With this passage, a slippage profile is generated, which represents the desired slippage during the passage. The slippage of the incoming torque transmission device is measured and controlled, in order to control the slippage of the incoming torque transmission device on the basis of the slippage speed profile.
The known solutions for influencing the quality of shifting in an automatic transmission are essentially characterized by a high expenditure for control and regulation technology. Further, in several variants, no immediate influencing of the shift quality is possible, on the basis of the secondary control strategy. Further, in the case of automatic transmissions, despite the influencing of the control pressure as a function of the determined travel characteristic values, only unsatisfactory results are obtained relative to quality of shifting.
The invention thus takes on the task of avoiding the named disadvantages and achieving a simple, automatic or self-learning adaptation of the shift processes under different operating conditions.
According to the invention, while not maintaining a specific time that can be given in advance for the beginning of the synchronization process or not maintaining a defined engine rpm change, the initial pressure value is adapted for introducing the necessary application force of the coupling parts that can be coupled together in a force-interlocking manner. In the case of these asynchronously shiftable couplings that usually transmit mechanically, at least two friction forces are pressed against one another, whereby a necessary friction for torque transmission is formed. Different basic geometrical forms are considered for use as the friction surfaces, for example friction discs, spherical and drum couplings, or the parallel connection of several friction units, for example, disc coupling. The torque that can be transmitted by friction in the case of these couplings that operate in a force-interlocking manner thus essentially depends, in addition to the application force, on the coefficient of friction as well as the number of pairs of friction surfaces. In a shift process, shiftable friction couplings are thus primary side and secondary side, i.e., input and output sides of the coupling, joined together by means of friction surfaces. Since the friction coefficient .mu. essentially changes during the slipping process as a consequence of the action of lubricant and heating, the course of the torque to be expected theoretically does not occur in practice. However, this course serves as the basis for the approximate calculation of slipping time and friction work. The slipping moment of the coupling acts as an acceleration moment and must also introduce the possibly acting effective moment. Since the friction work necessary in the shift process is also essentially converted to heat energy and thus leads to the heating of the coupling, and thus the friction surfaces are not disturbed as a consequence of the adjusting temperatures, limiting values are given in advance for the duration of slippage time at specific rpm values, depending on the coupling type and size. Too long a slippage time is reflected by an increased load of the friction elements, which leads to an increased wear and to an increased requirement for shift force.
According to the invention, the time for adjusting the control pressure value and thus also the time up to the beginning of the synchronization process is influenced by influencing the initial pressure value. This makes it possible to maintain a specific total time value for the shift process and simultaneously to also essentially improve the quality of shifting. The adaption of the initial pressure value according to the invention makes it possible to keep the load on the disc small.
For first-time operation, preferably for the first shift, approximately double pressure correction values are used. This assures a rapid adaptation of the shift pressure curve to the vehicle and the travel conditions. The correction values themselves may be stored in RAM or with larger deviations from the actually stored value also in EEPROM. This means that the last pressure correction values will be retained even after shutting off the ignition. Further, there is the possibility of blocking the adaptation, in case of errors in the sensory device, e.g., in the rpm sensor or load indicator. The shifting may be conducted with the control pressure characteristic fields entered in the EEPROM.
Essential advantages with the use of the adaption according to the invention consist of the fact that the control devices are independent of the transmission, and an adaptation on the test stand, which is economically very expensive, can be dispensed with. Further, an improved quality of shifting can be made possible by consideration of transmission, engine and vehicle parameters, in combination with maintaining a time given in advance up to the synchronization process for each load indicator value.
The adaption makes possible a uniform shift quality over the entire lifetime of the transmission despite variable operating conditions.